1. Technical Field
The present invention relates to a fuel cell usable for various usages such as electric sources and electric generators for outdoor, pleasure trip, household, business machines, or the like, and more particular, to an airbreathing fuel cell capable of supplying a sufficient amount of oxygen into cells in a pollution-free polymer electrolyte fuel cell.
2. Background Art
Among fuel cells, a polymer electrolyte fuel cell with hydrogen as a main fuel has been given attention and developed because of low working temperature and high power density. Examples of such fuel cells are described in U.S. Pat. No. 5,595,834 or JP-A 2002-270212 filed by the applicant of the present application.
As an example of such fuel cells, the inventors of the present application have proposed an airbreathing fuel cell, in which unit cells having a circular-shaped cross section are stacked. Concretely, a unit cell 10′ comprises, as shown in FIG. 9, an anode (fuel electrode) 13a and a cathode (oxygen electrode) 13b provided on both surfaces of a solid polymer electrolyte membrane 12, an oxygen passage plate 18′ provided adjacent and toward the oxygen electrode, and separator plates 34 arranged outside the fuel electrode 13a and outside the oxygen passage plate 18′ to unite these elements, and a plurality of such unit cells 10′ are stacked together so as to provide a cell stack as hereinafter referred to “a cell stack”. In addition, the separator plates 34 are provided with terminals, through which electricity generated is taken out, and serve as collecting plates. Further, a fuel distribution manifold 32 communicated to the fuel electrodes 13a and composed of a sleeve of hydrophilic synthetic fiber yarns is provided to extend through central holes of the unit cells 10, end plates 24 are further provided on both ends of a tie bolt 26, which extends centrally through the fuel distribution manifold 32, to interpose end gaskets 28 between the end plates 24 and the separator plates 34, and one nut 40 having fuel flow passages 44 and the other nut 50 having a breeder valve 52 interpose O-rings 36 between them and the end plates 24 to clamp and fix the unit cells integrally. Since such fuel cell can be made small in size and lightweight, it has been developed as a fuel cell of low power.
Also, such polymer electrolyte fuel cell is configured such that a fuel is fed from a center of the one nut 40 through the fuel flow passages 44 as shown with dash lines in FIG. 9 to be distributed to the fuel electrodes 13a through the hydrophilic synthetic fiber yarns sleeve of the fuel distribution manifold 32.
However, with such conventional solid polymer electrolyte fuel cell, oxygen is supplied to the oxygen electrodes 13b by supplying of a surrounding air through the porous oxygen passage plates 18, and in the case of a fuel cell of small electric power, supplying of an air for attaining the function of the cell is effected through holes of oxygen passage plates. However, an amount of oxygen supplied through such oxygen passage plates places a limit upon the power generating capacity, and therefore power generation cannot be performed to obtain an electric current according to uses.
Also, such airbreathing fuel cell is generally cylindrical-shape so that oxygen from the surrounding atmosphere is uniformly supplied to the oxygen electrodes through the oxygen passage plates, and thus the oxygen passage plates are made small in area to make a large resistance to passage of an air through the porous oxygen passage plates, so that oxygen cannot be supplied sufficiently to increase electric power generation.